I just tried taking on about 11 victories, 5 acclamators and about 11 or so broadsides with a better than equal amount of of assault frigates, cruisers, Antillies an ion cannon (raided and secured the planet) and a dozen Y-wings and ended up losing them all to destroy 7 of the victories a few acclamators and 4 broadsides. The war was over mon calamari with me appearing in the south west corner, surrounded by nebula to the east the north and the empire bringing it's full force on me and beginning to fire instantly. Naturally the assault frigates are way too slow to get clear of the nebula before getting wailed on by victories.

Now, I did do some research to choose that fleet to attack with from this site, and seen some people claim to beat worse odds with similar fleets and hardly take any losses, so I assume my technique is just terrible. I'm certainly no Thrawn, Tarkin or Ackbar when it comes to executing these battles, so any demo recordings or general tips on how to wipe the floor would be nice.

Well, it seems that you have a distinct lack of anti-fighter defense. Though Imperial bombers might not seem like much of a threat, they can be deadly enough and considering the odds, your opponent certainly has quite a few of them.

I, like many others, am not a fan of using Assault Frigates. Slow, ponderous and with as much firepower as a snail. You can spawn Regular Frigates which, although less effective then its larger cousin and relatively weak against Imperial warships, has the advantage of being easy to spam and cheap.

Anyway, let's play with what we have.

Try and hit the broadsides first. They're weak but can do massive damage, especially against your bomber force. As such, it's a good idea to spread out to avoid being caught by a massive barrage of their missiles.

The ion cannon is only useful to keep a Victory out of the battle for some time.

After wiping out the broadsides, try concentrating fire on one capital ship at a time. Personally, I'd go for the Acclamators first as they're slightly faster and can maneuver better against your ships.

Harass their fleet with your Y-Wing. Keep them on the move and as far away from Tie Fighters as possible. Your lack of ships able to protect them can sting here, though Antilles does provide some relief, it might not be enough against the numbers arrayed against you.

Remember that your capital ships are not the equal of the Empire. You do not have the advantage in equal numbers.